A. Field of the Invention
The present invention relates in general to so-called multi-mode radiotelephones that use SIM cards to store and access information. More particularly, the invention relates to a multi-mode radiotelephone having at least two master components and a single SIM card. A method and apparatus are provided for synchronizing and coordinating communications from either master component directly to the SIM card, thereby allowing a single SIM card to directly service two master components. The present invention has particular application to portable radiotelephones used to communicate with terrestrial cellular or satellite wireless telephony systems.
B. Description of Relevant Art
A Subscriber Identity Module (SIM) card is, in general, a smart card that is used in connection with cellular radiotelephones that follow the GSM cellular communications standard. Because they are smart cards, SIM cards are basically small computers that have their own processors. SIM cards generally contain a variety of information related to the subscriber, including, for example, a subscriber identifier, a phonebook identifying a stored bank of telephone numbers, voice messages, encryption sequences for secured data communications over the air, and other information. The SIM card can be removed from the phone and used by the subscriber on another phone, thereby allowing users the flexibility of being able to essentially take their "identity" with them from phone to phone.
A multi-mode radiotelephone that uses technology similar to the above-described SIM card is Motorola's Satellite Series 9500 Portable Telephone designed for use on the Iridium System (hereinafter "multi-mode phone"). The multi-mode characteristics of such a phone allow communication through either a satellite telephony network or a terrestrial cellular telephony network. It follows generally the GSM communication standard and therefore also uses a SIM card. For flexibility, the multi-mode phone is preferably modular, and its primary modular component is its base phone unit, which provides the main communication conduit between the user and the satellite-based telephony system. Various cellular cassette modules may be plugged into the base phone unit, with each cellular cassette module providing a communication conduit to a particular cellular system. For example plug-in cassettes are available that follow one of several cellular air interface standards developed/promulgated by the Telecommunications Industry Association, while another different plug-in cassette is available that follows the European GSM cellular standards. The base phone unit is essentially a complete radiotelephone including microprocessor, display, microphone, speakers and keypad. Each cellular cassette is also a substantially complete radiotelephone having the essentially the same components as the base phone unit minus the display and key-pad.
Thus, a multi-mode phone that uses a single SIM card, and that has plugged therein a cellular cassette based on the GSM standard, must allow information on the SIM card to be accessed by both the base phone unit and the cellular cassette. However, conventional SIM cards are designed to interact with and be accessed by only one device at a time. Because a SIM card has its own processor, and because the GSM standard generally requires a relatively elaborate scheme for communicating with a SIM card, interacting with and accessing data from the SIM card is more complicated than just reading data out from a RAM. Instead, the requesting device and the SIM card are actually exchanging commands and responses back and forth. However, the SIM card's processor is relatively simple and slow and does not have a clear concept of state. Therefore it is not designed to switch back and forth between commands received from different master devices. For example, assume that one master device instructs the SIM card to first enter a particular directory, enter an associated subdirectory, open a file in that subdirectory, and output a record in that subdirectory. If in the middle of executing these instructions, a second master device also needs to access data on the SIM card and therefore sends to the SIM card an instruction to go to a different directory, the SIM card would execute that instruction when received without reconciling it with the instructions that it received from the first master device.
Thus, SIM cards have, to date, been associated with and used by one master device, which is typically the phone in which the SIM card is housed. Other devices external to the phone may interact with and access information on a given SIM card, but such external devices typically access the SIM card indirectly by going through the phone in which the SIM card is housed. Accordingly, there is a need for a method and apparatus that allows two master devices to directly interact with and access information on a conventional SIM card.